<!DOCTYPE html>
<html>
<title>View transitions: promise resolution ordering</title>
<link rel="help" href="https://drafts.csswg.org/css-view-transitions-1/">
<link rel="author" href="mailto:vmpstr@chromium.org">

<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<style>
div {
  width: 100px;
  height: 100px;
  background: blue;
  contain: paint;
  view-transition-name: target;
}
.green {
  background: green;
}
</style>

<div id=target></div>

<script>
promise_test(async t => {
  assert_implements(document.startViewTransition, "Missing document.startViewTransition");
  return new Promise((resolve, reject) => {
    let dom_change_ran = false;
    let transition = document.startViewTransition(() => {
      target.classList.add("green");
      dom_change_ran = true;
    });

    let dom_updated_resolved = false;
    transition.updateCallbackDone.then(() => {
      if (!dom_change_ran)
        reject();
      // If there's a rAF before ready resolves, we fail.
      requestAnimationFrame(reject);
      dom_updated_resolved = true;
    });

    transition.ready.then(() => {
      if (!dom_updated_resolved)
        reject();
      resolve();
    });
  });
}, "updateCallbackDone resolves, then ready resolves with no rAF in between");
</script>
